1. Field of the Invention
The present invention relates to a control apparatus for a vehicle.
2. Description of Related Art
Nowadays, vehicles are equipped with various electronically controlled systems. For instance, in such a vehicle, as recited in Japanese Unexamined Patent Publication No. H06-149348A, in order to guarantee an operational reliability of the control system, an output signal of a sensor is inputted to two microcomputers, and these two computers execute an identical computation based on the common output signal of the sensor. Then, the computed results of these computers are compared with each other to determine whether an abnormality exists in the control system.
However, according to the technique of Japanese Unexamined Patent Publication No. H06-149348A, the two microcomputers, which execute the identical computation, need to be provided in the one control system. Therefore, it cannot meet the low cost demand, which is considered as the important technical goal in these days.
The inventor of the present invention has been working on a system which can guarantee an operational reliability of the control system through use of one microcomputer and one monitor integrated circuit (IC). Specifically, with reference to FIG. 5, in the microcomputer 13, a signal processing device 16 computes control signals (e.g., a signal indicating a sensed accelerator position value, a signal indicating a sensed throttle position value) based on output signals of sensors (e.g., an accelerator position sensor 11, a throttle position sensor 12) after the output signals of the sensors are processed through an analogue-to-digital (A/D) converter 15. Then, a torque control device 17 executes a control operation of actuators 14 (e.g., a throttle valve, a fuel injection valve, a spark plug) in such a manner that an actual torque of an internal combustion engine coincides with a requested torque based on the computed control signals. In such a control system, a torque monitor device 19 of the microcomputer 13 compares the actual torque and the requested torque based on the control signals and determines whether a torque increase abnormality (an abnormality, in which the actual torque becomes excessively large relative to the requested torque) exists. Furthermore, the monitor IC 21, which is provided separately from the microcomputer 13, monitors the operational state of the torque monitor device 19 and determines whether an operational abnormality of the torque monitor device 19 exists. In the experimental study of the above system, the following disadvantages have been identified.
In the torque control system of FIG. 5, although it is possible to guarantee the proper operation of the torque monitor device 19 with use of the monitor IC 21, there is no function, which guarantees the proper operation of the signal processing device 16. Therefore, in a case where the torque monitor device 19 functions property, when the abnormal value of the control signal (e.g., the sensed accelerator position value) is generated due to the operational abnormality of the signal processing device 16, the torque monitor device 19 determines whether the torque increase abnormality exists based on the abnormal control signal. Therefore, in a case where the torque increase abnormality actually exists, there is a high possibility of that such a torque increase abnormality cannot be sensed, and thereby the operational reliability of the control system cannot be sufficiently ensured.
In order to address the above disadvantage, as shown in FIG. 6, the monitor IC 21 may monitor the operational state of the signal processing device 16 and the operational state of the torque monitor device 19 and may determine whether the operational abnormality of the signal processing device 16 or of the torque monitor device 19 exists. In this way, the proper operation of the signal processing device 16 and the proper operation of the torque monitor device 19 can be guaranteed with the monitor IC 21.
However, in the torque control system shown in FIG. 6, the monitor IC 21 monitors the operational state of the signal processing device 16. Therefore, the signal processing device 16 needs to have an additional function of executing computation based on test data, which is used to test the operation of the signal processing device 16, and the monitor IC 21 needs to have an additional function of checking the computed result of the signal processing device 16, which is computed based on the test data. Therefore, the computational load is increased on the microcomputer 13 and the monitor IC 21. As a result, it is necessary to increase the computational performance of the microcomputer 13 and the computational performance of the monitor IC 21. Thus, in such a case, it is not possible to satisfy the low cost demand.